Steer-by-wire steering systems for motor vehicles have, as do known conventional steering systems, a steering column into which steering commands are input as usual by manual rotation of a steering wheel. The steering wheel brings about the rotation of a steering spindle which, however, is not connected mechanically via a steering gear to the wheels to be steered but instead senses the input steering command via rotational angle sensors or torque sensors and outputs an electrical control signal determined therefrom to a steering actuator which sets a corresponding steering lock of the wheels by means of an electric actuating drive.
The steering wheel is attached to the end of the steering spindle which is at the rear with respect to the direction of travel and faces the driver. Said steering spindle is held in a casing unit so as to be rotatable about the longitudinal axis of said steering spindle, which casing unit is for its part secured in a supporting unit which can be connected to the bodywork of the vehicle.
For the purpose of adaptation to the driver's position, adjustable steering columns in accordance with the generic type are known which permit adjustment of the steering wheel position relative to the bodywork of the vehicle. Longitudinal adjustment of the steering wheel in the direction of the longitudinal axis of the steering spindle can be implemented by virtue of the fact that the actuating unit is configured to have a variable length in that the casing unit has an arrangement of casing tubes which is telescopic in the direction of the longitudinal axis, i.e. axially, and in which, for example, the first casing tube is an outer casing tube in which a second casing tube is held so as to be movable axially as an inner casing tube.
The longitudinal adjustment of the steering column can be carried out by means of an actuating drive driven by an electric motor and comprising a spindle drive, in order to increase the ease of operator control. Since the threaded spindle of the spindle drive is connected to one of the casing tubes while being oriented parallel to the longitudinal axis, and since the spindle nut which can move in a translatory fashion with respect to the threaded spindle is connected in a rotationally fixed fashion to the other casing tube, the casing tubes can be moved in or out in the longitudinal direction depending on the direction of rotation of the actuating motor driving the threaded spindle. Such an arrangement is known in the prior art for a conventional steering column from, for example, DE 10 2014 101 995 A1.
In steer-by-wire steering systems, the need to make the steering shaft extend as far as the steering gear is dispensed with and therefore a design of the steering column which is as simple and compact as possible is aimed at, said design taking up little installation space and being able to be stowed in the smallest possible space, in particular for autonomous driving during which manual steering intervention is not required during travel. For safety reasons, as far as possible no moving or rotating parts of the spindle drive are to be accessible from the passenger compartment of the vehicle in this context. In this context, with previously known steering columns it is disadvantageous that the spindle drive is attached with an externally exposed threaded spindle to the casing unit. This already results in a relatively voluminous design which is made even larger by protection devices for the threaded spindle, and is therefore only suitable for steer-by-wire steering systems to a limited degree.
Thus a need exists for a steering column that can be adjusted by motor and that is more suitable for use in steer-by-wire steering systems. In particular, a need exists for a simple, compact and safe design.